1. Field of the Invention
The present invention relates to the production of dense ceramic materials which require alumina as either a densification aid or a matrix, and more particulary to the use of polymeric aluminum containing sols as coating material for ceramic powder as to the means of at least in partial process which resulted in green compacts with better microstructural homogeneity and excellent reproducibility.
2. Description of the Prior Art
Efforts have been focussed on preparing green compacts with microstructural homogeneity. It has been carried out through milling, dispersing, or spray-drying, and followed by forming green compacts by means of dry pressing, slip casting, or colloid pressing. Such prepared green compacts are subjected to densification by hot press, hot isostatic press, pressure or pressureless sintering. Alumina is added in the process of preparing green compacts as a powder or a colliodal sol wherein high purity submicron sized alumina is preferred.
Colloidal alumina sol or gel is disclosed by Yoldas in U.S. Pat. No. 3,944,658 (1976) and thereafter a few methods of preparing peptizable alumina are disclosed. In U.S. Pat. Nos. 4,574,003 (1986) and 4,801,399 (1989) water soluble inorganic salts (e.g. aluminum nitrate or zirconium nitrate) are disclosed as peptizing agents, herein colloidal sol is used for preparing alumina monoliths, alumina-based ceramic abrasive grains, or composites. The ceramic material which results from most, if not all, of these processes is well below its theoretical density.